1. Field of the Invention
The present invention relates to a rewinder with slitter for slitting a strip-like sheet of plastic film, paper or the like into a plurality of slit sheets to be wound on winding axles or winding cores which are mounted on the winding axles in an inserting manner.
2. Description of Prior Art
For good quality winding of the strip-like sheet on the winding axle into a roll shape by rotatably driving the winding axle, torque of the winding axle for adjusting winding tension of the strip-like sheet and contact pressure of a touch roller brought into contact with the roll of the strip-like sheet for adjusting the amount of air involved between sheet layers of the sheet roll in the winding operation on the winding axle are both important factors to be controlled. However, it is not necessarily possible to obtain a high quality wound sheet roll even if both the torque of the winding axle and the contact pressure between the sheet roll and the touch roller are precisely controlled.
The reason is that, for example, when the strip-like sheet taken off the roll of material by means of unwinding rollers (hereinafter referred to as "the take-our operation") is fed to its winding section to be wound on the winding axles, since the strip-like sheet to be fed to the winding section is already stretched within its elastic limit under the effect of the tension produced therein in the take-out operation, and the stretching of the strip-like sheet generally varies with every change of tension in the take-out operation due to deformation and the like of the material roll thereof, the stretching of the strip-like sheet produced immediately before its winding operation, i.e., residual stress, affects its winding tension.
For example, the stretching of the strip-like sheet already produced immediately before the winding operation is added to stretching produced under the effect of the tension of the strip-like sheet caused by the torque of the winding axle, and, as a result of this, the strip-like sheet is wound under excessive stretching. Consequently, inner layers of the sheet roll are compressed by the outer layers thereof under the effect of the contacting force of the strip-like sheet, producing a permanent set such as a lateral rumple therein so that the strip-like sheet is taken out or unwound in poor condition.
Therefore, in order to obtain a high quality wound sheet roll, it is essential to control the tension of the strip-like sheet immediately before it is wound on the winding axle, and to control the torque of the winding axle and the contact pressure between the touch roller and the sheet roll.
It has been proposed, for example in Japanese Patent Publication No. SHO 59(1984)-13414, that, because of the necessity of controlling the tension of the strip-like sheet immediately before it is wound, a rewinder with slitter controls the tension of a slit sheet S' immediately before it is wound by the powered rotation of a touch roller through a transmission mechanism for fine adjustment of its transmitting speed so as to be able to control the circumferential speed of the touch roller relative to the circumferential speed of the unwinding roller which unwinds a wide width of strip-like sheet from the material roll thereof, the touch roller being brought into contact with a plurality of the sheet rolls R for winding individual slit sheets.
On the other hand, there is a tendency to gradually vary the kind of the strip-like sheet to be slit and wound by means of the rewinder with slitter. For example, there is a tendency nowadays to progressively thin down a plastic film, and as a result a very thin one having a thickness of several tens of microns or of only a few microns is produced. In addition to this, many kinds of strip-like sheets are produced nowadays, some being easily stretchable even under low tension, others having a smooth surface such as a mirror finish and therefore having a low friction coefficient so that it easily slips etc.
Thin, easily stretched strip-like sheet is apt to rumple while the strip-like sheet which easily slips tends in the winding operation to suffer slippage of intermediate sheet layers axially to the sheet roll so that unevenness is produced on the ends of the roll though the upper layers of the sheet roll contacting the touch roller and the winding core of the sheet roll are held stationary.
Further, strip-like sheet varies in thickness. For example, plastic film of a thickness of 20 microns has a dimensional tolerance of thickness in the range of .+-.1 micron, or more in some cases. Nowadays, there is strongly felt need to wind strip-like sheet at high speed and with high quality.
On the other hand, regardless of the mechanical precision of the winder, some factors causing the wrinkling which deteriorates the winding quality of the sheet roll still exist in slitting and winding of the strip-like sheet. Such factors include: a concentration of tension in thicker portions of strip-like sheet of irregular thickness across its width during the movement thereof; concentration of tension in an area of the strip-like sheet leading to a larger diameter portion of the sheet roll, and as the larger diameter portion has a higher circumferential speed than the smaller diameter portion, the larger diameter portion pulls the strip-like sheet faster in such an area than in other areas, so the sheet roll varies slightly in its outer diameter along its axis, due to the superposition of sheets of irregular thickness as the sheets pile up on the roll; also, there is irregularity in tension distribution caused by deformation of the sheet roll in the initial stages of the winding operation due to flexing of the winding core of the sheet roll; and the like. Especially, wrinkling of the strip-like sheet in the direction of the sheet travel, or oblique wrinkling produced across the direction of travel of the strip-like sheet immediately before it is wound, is involved in the sheet roll, and as it folds and piles up, the outer diameter of the sheet roll increases over the wrinkling, causing build-up of contact pressure and tension, producing permanent strain in such portions, frequently deteriorating or ruining the value of the strip-like sheet as merchandise.
However, since it is substantially impossible to eliminate the factors causing the wrinkling, it is necessary to prevent wrinkling being produced even when such factors exist. From this necessity, various studies have been carried out. As a result, it has been found that the smaller the outer diameter of the touch roller, thus the smaller the radius of curvature of the strip-like sheet around the touch roller, the more difficult it is to deform the strip-like sheet axially to the touch roller, thus making it hard to produce wrinkles in the sheet wound on the winding axle.
However in the touch roller of the above-mentioned rewinder with slitter, since any of the contacting pressure loads of a plurality of the sheet rolls is applied to the touch roller and the span between the ends of the touch roller is considerable, it is not possible to reduce the outer diameter of the touch roller as this would affect its structural strength. For example, in a rewinder with slitter in which a width of the strip-like sheet unwinding from the roll is 6 m, the supporting span between the ends of the touch roller is approximately 7 m while its outer diameter is approximately 0.6 m.
Further, for preventing the wrinkling, it is necessary that the strip-like sheet which has been slit travels at a constant speed over its full width. However, it is not possible to precisely hold any portion of the slit sheet by means of the touch roller so that it travels at such a constant speed, because the adhesive force of the strip-like sheet to an outer peripheral surface of the touch roller is still smaller than in the case where a small diameter touch roller is employed, even when the same tension as that applied to the strip-like sheet contact with the small diameter touch roller is applied to the strip-like sheet running around the touch roller since the touch roller has a large outer diameter, as described above, and also because it is not possible to obtain sufficient frictional force between the slit strip-like sheet and the touch roller since air is apt to be entrained between the outer peripheral surface of the sheet roll and the strip-like sheet with the speed-up in the winding operation of the strip-like sheet, so that the frictional coefficient therebetween decreases.
Consequently, in a conventional rewinder with slitter provided with the touch roller, it is not possible to slit and wind the sheet and prevent wrinkling.
Further, in the case of strip-like sheet having a slipping surface, in order to prevent irregularities from being produced at the ends of the sheet roll, it is necessary to prevent air from being entrained between sheet layers, thereby preventing decrease of the frictional cofficient therebetween, and increasing the contacting pressure therebetween.
Since the outer diameter of the touch roller is large so that the contact area of the touch roller with respect to the sheet roll is large, to reduce the contact pressure per unit area therebetween, it is necessary to provide a large urging force between the touch roller and the sheet roll in order to increase the contact pressure therebetween. Further, when the winding operation is speeded up, the amount of air involved in the sheet roll is increased, making it necessary to further increase such urging force. However, when such urging force is further increased between the touch roller and the sheet roll, the sheet roll is deformed, increasing its resistance in rotation, and torque loss of the winding axle is increased, making control of the tension of the sheet in the winding operation unstable and often producing irregularity in the ends of the sheet roll thus wound.
Consequently, in some cases, it is not possible to obtain a sufficient contact pressure with such slippery strip-like sheet by means of the touch roller.
In such circumstances, the rewinder with slitter provided with the conventional touch roller does not necessarily meet the user''s level of requirements, because the thinner the strip-like sheet becomes the easier it stretches, and the more slippery its surface becomes the less the yield of quality-wound sheet roll.